Battery electrode substrate and process for producing the same

ABSTRACT

A battery electrode substrate which is constituted of a porous metallic body structure having communicating pores at a porosity of at least 90% and an Fe/Ni multilayer structure wherein the skeletal portion of the porous metallic body is composed mainly of Fe and has an Ni covering layer on the surface thereof while pores communicating with the inside and outside of Fe skeletal portion exist in the Fe skeletal portion and the inside of the pores is covered with Ni. The electrode substrate is produced by applying an iron oxide powder of at most 20 μm in an average particle size on a porous resin core body; heat treating the core to remove an organic resin component while simultaneously sintering Fe to obtain a porous Fe body; and then covering the Fe skeletal portion with Ni by electroplating. In this process, the iron oxide can be used in combination with carbon powder. Further, a nickel porous sintered body can also be produced using nickel oxide in place of iron oxide.

PRIOR APPLICATION

This application is a division of U.S. patent application Ser. No.717,191 filed Sep. 20, 1996 now U.S. Pat. No. 5,851,599.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for producing a porousmetallic material to be used as an electrode substrate for use in analkaline secondary battery principally such as a nickel-cadmium battery,a nickel-zinc battery or a nickel-hydrogen battery.

2. Description of the Prior Art

Storage batteries for use as various electric power sources include leadstorage batteries and alkaline storage batteries. Among them, thealkaline storage batteries have been widely used in various portableapparatuses in the form of a miniature battery and in industrialapplications in the form of a large-sized one, for example, because theycan be expected to be high in reliability and can be miniaturized to belightweight. In these alkaline storage batteries, materials for negativeelectrodes include zinc, iron, hydrogen, etc. in addition to cadmium.However, positive electrodes are nickel electrodes in almost all casesthough an air electrode, a silver oxide electrode, etc. are partiallyadopted. Replacement of a sintered type for a pocket type has attainedimprovements in properties and enabled hermetic sealing thereof to widenthe scope of uses thereof.

In a common powder-sintered type substrate, however, the strengththereof is greatly lowered when the porosity thereof is set to be atleast 85%. Thus, there is a limit to filling it with an active material.Accordingly, there is a limit to increasing the capacity of a battery.In view of the above, a foamed substrate and a fibrous substrate havebeen adopted and put into practical use as substrates having a farhigher porosity of at least 90% or the like in place of the sinteredsubstrate. Processes for producing such a high-porosity porous metallicbody substrate include a plating process as disclosed in Japanese PatentLaid-Open No. 174,484/1982, and a sintering process as disclosed inJapanese Patent Publication No. 17,554/1963 and the like. The platingprocess is a method wherein the skeletal surface of a foamed resin suchas a urethane foam is coated with a carbon powder or the like to effectsuch a treatment thereof as to be rendered electrically conductive, andfurther subjected to Ni electrodeposition by electroplating, followed byburning out the foamed resin and the carbon to obtain a porous metallicmaterial. On the other hand, according to the sintering process, theskeletal surface of a foamed resin such as a urethane foam is dipped inand coated with a slurry of a metal powder, followed by heating tosinter the metal powder.

As shown in the prior art, application of a porous metallic body to abattery plate substrate has made a great contribution to an increase inthe capacity of a battery. In production of a porous metallic bodyaccording to the plating process as disclosed in Japanese PatentLaid-Open No. 174,484/1982, however, a porous resin core body must becoated with carbon to effect such a treatment thereof as to be renderedelectrically conductive for electroplating. Carbon is necessary only ina step of production, but unnecessary in the porous metallic bodybecause it is finally burnt out. Thus, coating the core body with carbonfor such a treatment to make it electrically conductive not only entailsan increase in the cost of a product, but also is believed to affect thequality of the product because of residual carbon. In this respect, animprovement has been desired. On the other hand, the production of aporous metallic body according to the sintering process as disclosed inJapanese Patent Publication No. 17,554/1963 does not fundamentallyinvolve the above-mentioned problems, but can hardly secure desirableproperties such as mechanical strength properties and electricalproperties required of a battery plate substrate because dense sinteringof a skeletal portion in the form of a porous body is difficult. On theother hand, Japanese Patent Publication No. 4,136/1994, directed to aprocess for producing a porous iron catalyst carrier, also discloses amethod of obtaining a porous Fe body using an iron powder, an iron oxidepowder, etc. According to this method, however, no properties requiredof a battery electrode substrate can be secured like in the foregoingcases, for example, because none other than a porous sintered bodyhaving a coarse skeletal portion can be obtained.

SUMMARY OF THE INVENTION

Under such circumstances, an object of the present invention is toprovide a battery electrode substrate decreased in residual carboncontent and having excellent mechanical strength properties andelectrical properties, and a process for producing the same at a lowproduction cost.

As a result of intensive investigations, the inventors of the presentinvention have found out that it is important that an electrodesubstrate have an Fe/Ni multilayer structure made of a porous bodyhaving the skeletal portion thereof consisting mainly of Fe and havingthe surface thereof covered with Ni, provided that the inside ofcommunicating pores in Fe skeletal portion is covered with Ni as well;that it is important that iron oxide or nickel oxide having a controlledparticle size be used as a starting material powder in producing such anelectrode substrate; and that, in the case of an iron oxide powder, useof a carbon powder in combination therewith is advantageous. The presentinvention has been completed based on these findings.

Specifically, the present invention is directed to:

(1) a battery electrode substrate as an active material carrier for usein a battery collector, the battery electrode substrate beingconstituted of a porous metallic body structure having communicatingpores at a porosity of at least 90% and an Fe/Ni multilayer structurewherein the skeletal portion of the porous metallic body is composedmainly of Fe and has an Ni covering layer on the surface thereof whilepores communicating with the inside and outside of Fe skeletal portionexist in the Fe skeletal portion and the inside of the pores is coveredwith Ni;

(2) a process for producing a battery electrode substrate, comprising:applying an iron oxide powder of at most 20 μm in an average particlesize on a porous resin core body having the skeletal surface thereofmade tacky; effecting a heat treatment in a reducing atmosphere within atemperature range of 950° C. to 1,350° C. to remove an organic resincomponent while simultaneously sintering Fe to obtain a porous Fe bodyhaving a carbon content of at most 0.2% and a porosity of at least 90%;and then covering the surface of the Fe skeletal portion with Ni by Nielectroplating;

(3) a process for producing a battery electrode substrate, comprising:mixing an iron oxide powder of at most 20 μm in an average particle sizewith a binder resin and a diluent such as water or an organic solvent toprepare a slurry; applying the slurry on a porous resin core body andthen drying the same; thereafter effecting a heat treatment in areducing atmosphere within the temperature range of 950° C. to 1,350° C.to remove an organic resin component while simultaneously sintering Feto obtain a porous Fe body having a carbon content of at most 0.2% and aporosity of at least 90%; and then covering the surface of the Feskeletal portion thereof with Ni by Ni electroplating;

(4) a process for producing a battery electrode substrate, comprising:applying a powder mixture of a carbon powder and an iron oxide powder ofat most 20 μm in an average particle size on a porous resin core bodyhaving the skeletal surface thereof made tacky; effecting a heattreatment thereof in a nonoxidizing atmosphere within a temperaturerange of 850° C. to 1,250° C. to remove an organic resin component whilesimultaneously sintering Fe to obtain a porous Fe body having a carboncontent of at most 0.2% and a porosity of at least 90%; and thencovering the surface of the Fe skeletal portion with Ni by Nielectroplating;

(5) a process for producing a battery electrode substrate, comprising:mixing a carbon powder and an iron oxide powder of at most 20 μm in anaverage particle size with a binder resin and a diluent such as water oran organic solvent to prepare a slurry; applying the slurry on a porousresin core body and then drying the same; thereafter effecting a heattreatment in a nonoxidizing atmosphere within a temperature range of850° C. to 1,250° C. to remove the organic resin component whilesimultaneously sintering Fe to obtain a porous Fe body having a carboncontent of at most 0.2% and a porosity of at least 90%; and thencovering the surface of the Fe skeletal portion with Ni by Nielectroplating;

(6) a process for producing a battery electrode substrate, comprising:mixing an iron oxide powder of at most 20 μm in an average particle sizewith a binder resin and a diluent such as water or an organic solvent toprepare a slurry in such a way that the residual carbon rate of thebinder resin and the blending proportion of the binder resin to the ironoxide satisfy the relationship of the following formula; applying theslurry on a porous resin core body and then drying the same; thereaftereffecting a heat treatment in an atmosphere of an inert gas at atemperature of 900° C. to 1,250° C. to carbonize the binder resin whilereduction-sintering iron oxide with the resulting carbonization product;thereafter effecting a heat treatment for reduction-sintering thenonreduced part of iron oxide in a reducing atmosphere at a temperatureof 900° C. to 1,350° C. to remove the organic resin component whilesimultaneously sintering Fe to obtain a porous Fe body having a carboncontent of at most 0.2% and a porosity of at least 90%; and thencovering the surface of the Fe skeletal portion thereof with Ni by Nielectroplating:

    3<a×b<11

a: residual carbon rate % of binder resin, provided that a >30

b: amount of the binder resin blended/amount of iron oxide blended;

(7) a process for producing a battery electrode substrate as set forthin any one of (2) to (5) above, wherein the thickness of the resultingNi covering layer is 0.1 μm to 10 μm;

(8) a process for producing a battery electrode substrate as set forthin any one of (2) to (5) above, wherein the iron oxide powder has anaverage particle size of at most 3 μm;

(9) a process for producing a battery electrode substrate as set forthin (4) or (5) above, wherein the amount of the carbon powder is 0.1 wt.% to 20 wt. % based on the iron oxide powder;

(10) a process for producing a battery electrode substrate, comprising:applying an Ni oxide powder of at most 20 μm in an average particle sizeon a porous resin core body having the skeletal surface thereof madetacky; and effecting a heat treatment in a reducing atmosphere withinthe temperature range of 900° C. to 1,300° C. to remove an organic resincomponent while simultaneously sintering Ni to form a porous Ni bodyhaving a carbon content of at most 0.2% and a porosity of at least 90%;

(11) a process for producing a battery electrode substrate, comprising:mixing an Ni oxide powder of at most 20 μm in an average particle sizewith a binder resin and a diluent such as water or an organic solvent toprepare a slurry; applying the slurry on a porous resin core body andthen drying the same; and thereafter effecting a heat treatment in areducing atmosphere within the temperature range of 900° C. to 1,300° C.to remove the organic resin component while simultaneously sintering Nito form a porous Ni body having a carbon content of at most 0.2% and aporosity of at least 90%; and

(12) a process for producing a battery electrode substrate as set forthin (10) or (11), wherein the Ni oxide powder has an average particlesize of at most 3 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a microscopic photograph of a battery electrode substrate ofthe present invention wherein the skeletal portion consisting mainly ofFe has the surface thereof covered with Ni.

FIG. 2 is a model cross-sectional view of the Fe skeletal portion asshown in FIG. 1, which view is perpendicular to the longitudinaldirection thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The battery electrode substrate of the present invention ischaracterized in that the porous body structure thereof as shown in FIG.1 has the skeletal portion 1 thereof made mainly of Fe and having an Nicovering layer 2 on the surface thereof, and that pores 3 communicatingwith the interior and surface thereof exist in the Fe skeletal portionin which the inside of the pores 3 covered with an Ni layer 4, as shownin FIG. 2, which is a model cross-sectional view of the skeletal portion1 which view is perpendicular to the longitudinal direction thereof.

In producing a battery plate substrate as a collector of a porousmetallic body, a part of the skeletal portion of the porous body isinevitably fractured in a pressing step, a winding step in the case of acylindrical battery, etc. after filling thereof with an active materialas a reactive substance in a battery. In the case of an Fe/Ni multilayerstructure, no problems arise in the surface of the skeletal portioncovered with Ni. However, Fe-exposed parts unavoidably exist on thefractured cross sections of the skeletal portion. The Fe-exposed partsare corroded in an electrolyte in a battery to cause self-discharge anddeterioration of life properties due to dissolution out of Fe as well asdeterioration of current collection properties due to formation ofnonconducting films, etc. to thereby lower the performance of thebattery.

It has however been found out that the areas of the Fe-exposed parts arerelatively decreased even in the fractured cross-sectional parts in thestructure of the present invention to enable the lowering of theperformance of a battery to be suppressed because an Ni covering layeris formed also on the inside of the Fe skeletal portion via thecommunicating pores.

The process of the present invention for producing a battery electrodesubstrate, which will now be described in detail, makes a great featureof using an iron oxide powder to form a porous Fe body portion throughreduction sintering thereof. Specifically, channels of gas formed duringthe reduction of iron oxide form communicating pores in the final porousFe body, and the walls of these pores are covered with Ni through Nielectroplating to obtain the structure of the present invention.

In the process of the present invention for producing a batteryelectrode substrate, employable methods of imparting tack to a porousresin core body include a method wherein a porous resin core body isdipped in a liquid mixture of a binder resin and a diluent such as wateror an organic solvent and then stripped of an excess of the attachedcomponent with rolls or the like, and a method wherein theabove-mentioned liquid mixture is sprayed on a porous resin core bodywith a spray. On the other hand, employable methods of application ofthe iron oxide powder, the powder mixture of the carbon powder and theiron oxide powder, or the nickel oxide powder include a method whereinthe powder is sprayed on a porous resin with an air gun, and a methodwherein the porous resin core body is swayed in the powder.

On the other hand, methods of slurrying the iron oxide powder, thepowder mixture of the carbon powder and the iron oxide powder, or thenickel oxide powder include a method wherein the iron oxide powder, thepowder mixture of the carbon powder and the iron oxide powder, or thenickel oxide powder is mixed with a binder resin, usable examples ofwhich include acrylic resins and phenolic resins, and a diluent such aswater or an organic solvent at a predetermined mixing proportion,followed by stirring, whereby a slurry can be prepared. Employablemethods of applying the slurry on the porous resin core body include amethod wherein a porous resin is impregnated with the slurry and thenstripped of an excess of the impregnating component with squeeze rolls,and a method wherein the slurry is sprayed with a spray.

Next, the porous resin coated with the iron oxide powder or the nickeloxide powder according to one of the foregoing methods is heat-treatedin a reducing atmosphere to remove the organic resin component includingthe resin core body and the binder resin while simultaneously reducingiron oxide to iron or nickel oxide to nickel and sintering the iron ornickel.

The average particle size of the iron oxide or nickel oxide powder to beused in the present invention is preferably at most 20 μm, stillpreferably at most 5 μm, further preferably at most 3 μm. In the case ofusing the powder mixture of the carbon powder and the iron oxide powder,the most preferable particle size of the iron oxide powder is at most 1μm.

When the average particle size exceeds 20 μm, the complete reduction ofiron oxide to iron or nickel oxide to nickel is time-consuming toprolong the heat treatment time, thereby not only presenting a practicalproblem of high production cost but also involving insufficientreduction, because of which dense sintering of the skeletal portioncannot be secured to lower the mechanical properties and electricalproperties thereof, leading to a failure in securing properties requiredof a battery electrode substrate.

Use of a particulate powder having an average particle size of at most 5μm as the iron oxide powder or the nickel oxide powder further produces,for example, such effects that (1) dense and uniform application on theporous resin core body is possible, that (2) reduction to iron or nickelcan be easily effected in a short time, and that (3) reduced iron ornickel is so particulate as well and hence so good in sinteringproperties as to obtain a dense sintered body. Further, as opposed tothe use of an iron powder or a nickel powder as a starting material asin the prior art, the use of the iron oxide powder or the nickel oxidepowder in the present invention gives the following important functionsand effects:

(4) Oxygen formed during the reduction of iron oxide or nickel oxidereacts with the organic resin component including the resin core bodyand the binder resin to yield carbonic acid gas, whereby the organiccomponent can be efficiently removed. Where a heat treatment is effectedin a reducing atmosphere, a part of the organic resin component usuallyremains in a carbonized form to effect solid solution into the porousmetallic body to thereby present a problem of adversely affecting theelectric resistance and strength properties thereof, as well as to beattached as soot to a furnace wall to thereby present a problem ofmaking the maintenance of a heat treatment furnace necessary. Theseproblems have however been solved according to the present invention.

(5) A particulate iron powder involves a risk of ignition, explosion,etc., and hence needs precaution in handling thereof. Further, thepowder itself is expensive. By contrast, a particulate iron oxide powderis inexpensive and easy of handling.

On the other hand, in the case of using the powder mixture of the carbonpowder and the iron oxide powder, the particle size of the carbon powderis preferably at most 20 μm, still preferably at most 5 μm.

In an embodiment of the present invention wherein use is made of apowder mixture of carbon powder and iron oxide powder, it has been foundout that addition of the carbon powder more easily promotes thereduction reaction of iron oxide to enable lowering of the sinteringtemperature and shortening of the sintering time. The amount of carbonto be added is preferably 0.1 wt. % to 20 wt. % based on iron oxide.When it is smaller than 0.1 wt. %, the effect of lowering the sinteringtemperature and shortening the sintering time by addition of carbon isnot observed. When it exceeds 20 wt. %, carbon remains in the resultingsintered body to deteriorate the strength properties and electricalproperties thereof because it exceeds the necessary amount for reductionof iron oxide by a great deal.

Examples of the atmosphere to be used in the heat treatment according tothe present invention include hydrogen gas, a decomposition gas ofammonia, a mixed gas of hydrogen and nitrogen, and nitrogen gas. In thecase of iron oxide, the heat treatment temperature is set to be 950° C.to 1,350° C. as the necessary temperature for reduction and sintering.Herein, when the temperature is lower than 950° C., reduction andsintering do not sufficiently proceed. When it exceeds 1,350° C., theporous skeletal structure cannot be maintained and hence turns into aflat plate sintered body. Further, it is still preferably 1,100° C. to1,300° C. In the case of using a powder mixture of carbon powder andiron oxide powder, the heat treatment temperature is set to be 850° C.to 1,250° C., preferably 950° C. to 1,150° C. On the other hand, in thecase of nickel oxide powder, it is 900° to 1,300° C., preferably 1,000°to 1,250° C.

Further, the following process is proposed as a preferred embodiment ofthe present invention with a view to realizing electrical properties andmechanical properties required of a battery electrode substrate evenaccording to a continuous heat treatment mode involving a rapid heat-upstage for increasing the throughput in the sintering step.

In the step of mixing iron oxide powder with a binder resin and adiluent such as water or an organic solvent to form a slurry, it ispreferred that the residual carbon rate of the binder resin and theblending proportion of the binder resin to iron oxide satisfy therelationship of the following formula:

    3<a×b<11

a: residual carbon rate % of the binder resin, provided that a>30

b: amount of the binder resin blended/amount of iron oxide blended

Herein, the term "residual carbon rate" means the percentage (%) of theresidual carbon content with respect to the initial weight of the binderresin measured according to the method specified in JIS (JapaneseIndustrial Standard) 2270.

On the other hand, the heat treatment of the porous resin core bodycoated with the slurry for formation of an Fe-sintered porous bodypreferably comprises a first step of heat treatment to be effected in anatmosphere of an inert gas at 900° C. to 1,250° C. to carbonize thebinder resin while reduction-sintering iron oxide with the resultingcarbonization product, and a subsequent second step of heat treatment tobe effected in an atmosphere of a reducing gas at a temperature of 900°C. to 1,350° C. to reduction-sinter the nonreduced part of iron oxide.Herein, N₂, Ar, etc. can be used as the inert gas, while H₂, NH₃, etc.can be used as the reducing gas. In the continuous heat treatment mode,works are rapidly heated up at a rate of 100° C./min or more because theworks are continuously introduced into a furnace heated up to apredetermined temperature. In the course of such rapid heat-up, theporous resin core body coated with the iron oxide slurry may sometimesbe burnt out at a stroke to vanish the skeletal structure-maintainingbody of the porous body. In such a case, since the structure-maintainingbody disappears before reduction sintering of the iron oxide powder,none other than an Fe sintered body having a large number of fracturedskeletal parts can be obtained, resulting in a failure in securingdesired properties as an electrode substrate. In view of the above,according to a preferred embodiment of the present invention, there isproposed a method wherein a skeletal structure-maintaining body issecured through carbonization of the binder resin after the porous resincore body is burnt out. For that purpose, it has been found out that theresidual carbon rate of the binder resin and the blending proportionthereof to iron oxide must satisfy the relationship of the foregoingformula. Herein, when a is lower than 30% or when a×b is smaller than 3,the carbonization product is so insufficient in functioning as theskeleton-maintaining body that desired properties cannot be secured dueto an increase in skeletal fracture. On the other hand, when a×b exceeds11, it has been found out that an excess of the carbonization productover that required for complete reduction of iron oxide remains toinhibit sintering of Fe formed through reduction, whereby a densesintered body cannot be obtained with great decreases in the strengthproperties etc. thereof.

Further, as for the steps of heat treatment, it is an importantrequirement to effect the first step thereof in an atmosphere of aninert gas. In the first step of heat treatment, carbonization of thebinder resin and reduction sintering of iron oxide only with thecarbonization product are effected. This enables not only the skeletalstructure to be maintained after the resin core body is burnt out, butalso the carbonization product, which finally becomes unnecessary, to beconsumed by reduction of iron oxide. At the point of time of completionof the first step, almost all the carbonization product has been removedwhile obtaining a composite sintered body of Fe and iron oxide bypartial reduction of the iron oxide powder. In the subsequent secondstep of heat treatment, the nonreduced iron oxide is completely reducedwith the atmosphere of the reducing gas while allowing the sintering ofFe to proceed.

According to the foregoing method, a porous Fe body structure withlittle skeletal fracture can be obtained even in the continuous heattreatment mode involving a stage of rapid heat-up, whereby electricalproperties and mechanical properties required of a battery electrodesubstrate can be realized.

According to the foregoing procedure, a porous iron or nickel bodyhaving a carbon content of at most 0.2% and a porosity of at least 90%can be obtained. Herein, since the carbon content is low due to theaforementioned effect of using the iron oxide powder or the nickel oxidepowder, a porous iron or nickel body having a good electric conductivityand excellent mechanical strengths such as elongation properties inparticular can be obtained, wherein properties required of a batteryelectrode substrate can be secured.

Next, the porous iron body obtained according to the foregoing method isNi-electroplated to form an Ni film and to thereby obtain a porousmetallic body having a strong corrosion resistance in a stronglyalkaline solution in an alkaline secondary battery in particular. AfterNi electroplating, it is preferably further heat-treated in anonoxidizing atmosphere to enable an improvement in the adhesion of theNi film and relaxation of residual stress due to the plating. Herein,the heat treatment temperature is preferably at most 600° C. On theother hand, the thickness of the Ni film is preferably 0.1 μm to 10 μm.When it is smaller than 0.1 μm, no sufficient corrosion resistance canbe secured. When it exceeds 10 μm, the porosity becomes lower. It isstill preferably at least 1 μm.

EXAMPLE 1

A polyurethane foam of 2.5 mm in thickness wherein the number of poresper inch was about 50 was dipped in a binder resin liquid prepared bymixing 60 wt. % of an acrylic resin with 40 wt. % of water, and thenstripped of an excess of the dip coating component with squeeze rolls toform a porous resin core body coated with the binder. Subsequently, anα-Fe₂ O₃ powder as shown in Table 1 was directly sprayed on the porousresin core body with an air gun, followed by drying in the air at 150°C. for 5 minutes. On the other hand, a sample (No. 8) as comparativeexample was also formed using an iron powder. Subsequently, a heattreatment was effected in a hydrogen stream at 1,280° C. for 10 minutesfor sintering to form porous Fe bodies. The properties of these porousFe bodies were evaluated. The results are shown in Table 2.

                  TABLE 1    ______________________________________    Sample No.   Average Particle Size (μm)    ______________________________________    1            0.8    2            2.1    3            4.5    4            10.5    5            17    6            40    7            100    8            40          (iron powder)    ______________________________________

                  TABLE 2    ______________________________________          Carbon           Electric Tensile    Sample          Content  Porosity                           Resistance                                    Strength                                            Elongation    No.   (wt. %)  (%)     (mΩ/100 mm)                                    (kg/15 mm)                                            (%)    ______________________________________    1     0.05     95      52       3.1     4.5    2     0.03     95      53       3.2     4.8    3     0.08     94      61       2.4     2.6    4     0.05     94      65       2.2     2.2    5     0.07     94      69       2.1     2.0    6     0.09     93      77       1.4     1.5    7     0.04     90      83       1.3     1.2    8     0.5      94      120      1.2     1.1    ______________________________________     Electric Resistance: electric resistance for a width of 10 mm and a lengt     of 100 mm.

EXAMPLE 2

The samples of Example 1 were Ni-plated in an Ni electroplating Wattsbath at an electric current density of 10 A/dm² to form Ni films of 2 μmin thickness. The properties of the resulting samples are shown in Table3.

                  TABLE 3    ______________________________________          Carbon           Electric Tensile    Sample          Content  Porosity                           Resistance                                    Strength                                            Elongation    No.   (wt. %)  (%)     (mΩ/100 mm)                                    (kg/15 mm)                                            (%)    ______________________________________    1     0.05     94      41       3.4     4.4    2     0.03     94      43       3.5     4.7    3     0.08     93      51       2.5     2.7    4     0.05     93      56       2.3     2.1    5     0.07     93      60       2.2     2.1    6     0.09     92      68       1.5     1.4    7     0.04     89      75       1.4     1.3    8     0.5      93      112      1.3     1.2    ______________________________________     Electric Resistance: electric resistance for a width of 10 mm and a lengt     of 100 mm.

Subsequently, the substrates shown in the table were used to producenickel electrodes for use in Ni-hydrogen batteries. They were filledwith an active material principally comprising nickel hydroxide, and thesurfaces thereof were then smoothed, followed by drying at 120° C. for 1hour. The resulting electrodes were pressed under a pressure of 1ton/cm² to have a length of 180 mm, a width of 220 mm and a thickness of0.7 mm.

5 nickel electrodes for each sample, 6 conventional MmNi (misch metalnickel) hydrogen occlusion alloy electrodes as counterpart electrodes,and a polypropylene nonwoven fabric separator treated to be renderedhydrophilic were used to constitute a square-shaped closednickel-hydrogen battery. An aqueous solution of caustic potash having aspecific gravity of 1.3 containing 25 g/l of lithium hydroxide dissolvedtherein was used as the electrolyte. Batteries Nos. 1B, 2B, 3B, . . .correspond to respective Samples Nos. in Table 3.

Each battery was examined with respect to discharge voltage and capacityat discharge currents of 10 A and 150 A, and was further evaluated withrespect to capacity retention rate (%) after 500 cycles each involving a10 A discharge in a life test. The results are shown in Table 4.

                  TABLE 4    ______________________________________                                    Capacity                                    Retention                         150        Rate    Battery  10 A Discharge                         A Discharge                                    after 500    No.     V        Ah     V      Ah   Cycles (%)    ______________________________________    1B      1.24     121    1.18   119  94    2B      1.24     120    1.18   119  94    3B      1.22     117    1.17   111  94    4B      1.21     115    1.15   110  92    5B      1.21     114    1.14   108  91    6B      1.12     108    1.03   97   89    7B      1.11     106    1.03   96   89    8B      1.11     104    0.98   93   87    ______________________________________

It has become apparent from the foregoing results that the batteryelectrode substrate of the present invention exhibits excellentproperties.

EXAMPLE 3

Sample 2 of Example 1 was used to form substrates with varied Ni filmthicknesses, which were used to produce Ni-hydrogen batteries accordingto the same procedure as in Example 2. They were examined with respectto capacity retention rate after 500 cycles each involving a 10 Adischarge. The results are shown in Table 5.

                  TABLE 5    ______________________________________    Ni Film       Capacity Retention    Thickness (μm)                  Rate (%)    ______________________________________    0.02          72    0.2           90    1.5           93    4.5           94    ______________________________________

EXAMPLE 4

50 wt. % of an Fe₃ O₄ powder as shown in Table 6 was blended with 10 wt.% of an acrylic resin, 2 wt. % of carboxymethylcellulose and 38 wt. % ofwater. The blend was mixed with a ball mill for 12 hours to prepare aslurry. Subsequently, a polyurethane foam of 2.5 mm in thickness whereinthe number of pores per inch was about 50 was dipped in the slurry,stripped of an excess of the attached component by roll squeezing, anddried in the air at 120° C. for 5 minutes to prepare a porous resincoated with the Fe₃ O₄ powder, which was then heat-treated in a hydrogenstream at 1,220° C. for 10 minutes for sintering to form a porous Febody. The properties of such porous Fe bodies were evaluated. Theresults are shown in Table 7.

                  TABLE 6    ______________________________________    Sample No.  Average Particle Size (μm)    ______________________________________    9           1.2    10          2.5    11          15    12          130    ______________________________________

                  TABLE 7    ______________________________________          Carbon           Electric Tensile    Sample          Content  Porosity                           Resistance                                    Strength                                            Elongation    No.   (wt. %)  (%)     (mΩ/100 mm)                                    (kg/15 mm)                                            (%)    ______________________________________    9     0.04     95      55       3.2     4.2    10    0.03     94      54       3.3     4.4    11    0.05     93      62       2.3     2.5    12    0.02     90      78       1.2     1.0    ______________________________________     Electric Resistance: electric resistance for a width of 10 mm and a lengt     of 100 mm.

Samples shown in Table 7 were Ni-plated in an Ni electroplating Wattsbath at an electric current density of 12 A/dm² to form Ni films of 3 μmin thickness. The properties of the resulting samples are shown in Table8.

                  TABLE 8    ______________________________________          Carbon           Electric Tensile    Sample          Content  Porosity                           Resistance                                    Strength                                            Elongation    No.   (wt. %)  (%)     (mΩ/100 mm)                                    (kg/15 mm)                                            (%)    ______________________________________    9     0.04     94      40       3.5     4.2    10    0.03     93      41       3.6     4.3    11    0.05     92      55       2.6     2.3    12    0.02     89      68       1.3     1.2    ______________________________________     Electric Resistance: electric resistance for a width of 10 mm and a lengt     of 100 mm.

Subsequently, Ni-hydrogen batteries were produced according to the sameprocedure as in Example 2, and the properties thereof were evaluated.The results are shown in Table 9.

                  TABLE 9    ______________________________________                                    Capacity                                    Retention                         150        Rate    Battery  10 A Discharge                         A Discharge                                    after 500    No.     V        Ah     V      Ah   Cycles (%)    ______________________________________     9B     1.24     123    1.19   120  94    10B     1.24     121    1.18   119  94    11B     1.21     116    1.16   110  94    12B     1.15     110    1.10   104  93    ______________________________________

EXAMPLE 5

A polyurethane foam of 2.5 mm in thickness wherein the number of poresper inch was about 50 was spray-coated with a binder resin liquidprepared by mixing 70 wt. % of a phenolic resin with 30 wt. % of waterto form a porous resin core body coated with the binder. Subsequently,the porous resin core body was swayed in an NiO powder as shown in Table10 to coat it with the NiO powder. On the other hand, a sample (No. 13)as a comparative example was also formed using an Ni powder.Subsequently, they were heat-treated in a hydrogen stream at 1,180° C.for 10 minutes for sintering to form porous Ni bodies. The properties ofthese porous Ni bodies were evaluated. The results are shown in Table11.

                  TABLE 10    ______________________________________    Sample No.  Average Particle Size (μm)    ______________________________________    13          1.2    14          5.6    15          18    16          60    ______________________________________

                  TABLE 11    ______________________________________          Carbon           Electric Tensile    Sample          Content  Porosity                           Resistance                                    Strength                                            Elongation    No.   (wt. %)  (%)     (mΩ/100 mm)                                    (kg/15 mm)                                            (%)    ______________________________________    13    0.01     95      39       3.3     4.5    14    0.02     94      38       3.1     4.8    15    0.01     93      46       2.5     2.6    16    0.01     90      63       1.5     1.1    ______________________________________     Electric Resistance: electric resistance for a width of 10 mm and a lengt     of 100 mm.

EXAMPLE 6

50 wt. % of an NiO powder as shown in Table 12 was blended with 10 wt. %of a phenolic resin, 2 wt. % of carboxymethylcellulose and 38 wt. % ofwater. The blend was mixed with a ball mill for 12 hours to prepare aslurry. Subsequently, a polyurethane foam of 2.5 mm in thickness whereinthe number of pores per inch was about 50 was dipped in the slurry,stripped of an excess of the attached component by roll squeezing, anddried in the air at 120° C. for 5 minutes to prepare a porous resincoated with the NiO powder, which was then heat-treated in a hydrogenstream at 1150° C. for 10 minutes for sintering to form a porous Nibody. The properties of such porous Ni bodies were evaluated. Theresults are shown in Table 13.

                  TABLE 12    ______________________________________    Sample No.  Average Particle Size (μm)    ______________________________________    17          1.5    18          8.6    19          15    20          35    ______________________________________

                  TABLE 13    ______________________________________          Carbon           Electric Tensile    Sample          Content  Porosity                           Resistance                                    Strength                                            Elongation    No.   (wt. %)  (%)     (mΩ/100 mm)                                    (kg/15 mm)                                            (%)    ______________________________________    17    0.02     94      38       3.1     4.1    18    0.03     93      39       3.5     4.0    19    0.02     93      45       2.6     2.3    20    0.03     92      59       1.7     1.2    ______________________________________     Electric Resistance: electric resistance for a width of 10 mm and a lengt     of 100 mm.

EXAMPLE 7

Samples shown in Tables 11 and 13 were used to produce Ni-hydrogenbatteries according to the same procedure as in Example 2, and theproperties thereof were evaluated. The results are shown in Table 14.

                  TABLE 14    ______________________________________                                   Capacity Retention    Battery           10 A Discharge                       150 A Discharge                                   Rate after    No.    V       Ah      V     Ah    500 Cycles (%)    ______________________________________    13B    1.24    121     1.20  120   94    14B    1.23    120     1.19  119   94    15B    1.21    117     1.14  114   94    16B    1.13    109     1.08  102   93    17B    1.24    122     1.19  121   94    18B    1.22    118     1.18  116   94    19B    1.20    117     1.18  115   93    20B    1.16    115     1.14  110   93    ______________________________________

EXAMPLE 8

A polyurethane foam of 2.5 mm in thickness wherein the number of poresper inch was about 50 was dipped in a binder resin liquid prepared bymixing 60 wt. % of an acrylic resin with 40 wt. % of water, and thenstripped of an excess of the dip coating component with squeeze rolls toform a porous resin core body coated with the binder. Subsequently, apowder mixture of an α-Fe₂ O₃ powder as shown in Table 15 and a graphitepowder of 5 μm in an average particle size was directly sprayed on theporous resin core body with an air gun, followed by drying in the air at150° C. for 5 minutes. On the other hand, a sample (No. 27) as acomparative example was also formed using an iron powder in place of theiron oxide powder. In passing, the carbon powder was mixed in an amountof 5 wt. % based on the iron oxide (iron) powder.

Subsequently, a heat treatment was effected in a hydrogen stream at1,050° C. for 5 minutes for sintering to form porous Fe bodies. Theproperties of these porous Fe bodies were evaluated. The results areshown in Table 16.

                  TABLE 15    ______________________________________    Sample No.   Average Particle Size (μm)    ______________________________________    21           0.6    22           1.5    23           4.5    24           15    25           50    26           150    27           50          (iron powder)    ______________________________________

                  TABLE 16    ______________________________________          Carbon           Electric Tensile    Sample          Content  Porosity                           Resistance                                    Strength                                            Elongation    No.   (wt. %)  (%)     (mΩ/100 mm)                                    (kg/15 mm)                                            (%)    ______________________________________    21    0.05     95      48       3.5     4.9    22    0.04     95      50       3.4     4.5    23    0.09     94      60       2.6     2.8    24    0.08     94      68       2.3     2.2    25    0.09     93      85       1.6     1.5    26    0.03     90      96       1.2     1.1    27    0.7      94      120      1.2     1.0    ______________________________________     Electric Resistance: electric resistance for a width of 10 mm and a lengt     of 100 mm.

EXAMPLE 9

The samples of Example 8 were Ni-plated in an Ni electroplating Wattsbath at an electric current density of 10 A/dm² to form Ni films of 2 μmin thickness. The properties of the resulting samples are shown in Table17.

                  TABLE 17    ______________________________________          Carbon           Electric Tensile    Sample          Content  Porosity                           Resistance                                    Strength                                            Elongation    No.   (wt. %)  (%)     (mΩ/100 mm)                                    (kg/15 mm)                                            (%)    ______________________________________    21    0.05     94      37       3.6     4.9    22    0.04     94      40       3.5     4.7    23    0.09     93      51       2.7     2.8    24    0.08     93      59       2.5     2.2    25    0.09     92      73       1.7     1.6    26    0.03     89      88       1.3     1.2    27    0.7      93      112      1.3     1.0    ______________________________________     Electric Resistance: electric resistance for a width of 10 mm and a lengt     of 100 mm.

Subsequently, the substrates shown in Table 17 were used to producenickel electrodes for use in Ni-hydrogen batteries. They were filledwith an active material principally comprising nickel hydroxide, and thesurfaces thereof were then smoothed, followed by drying at 120° C. for 1hour. The resulting electrodes were pressed under a pressure of 1ton/cm² to have a length of 190 mm, a width of 210 mm and a thickness of0.7 mm.

5 nickel electrodes for each sample, 6 conventional MmNi (misch metalnickel) hydrogen occlusion alloy electrodes as counterpart electrodes,and a polypropylene nonwoven fabric separator treated to be renderedhydrophilic were used to constitute a square-shaped closednickel-hydrogen battery. An aqueous solution of caustic potash having aspecific gravity of 1.3 containing 25 g/l of lithium hydroxide dissolvedtherein was used as the electrolyte. Batteries Nos. 21B, 22B, 23B, . . .correspond to respective Samples Nos. in Table 17.

Each battery was examined with respect to discharge voltage and capacityat discharge currents of 10 A and 150 A, and was further evaluated withrespect to capacity retention rate after 500 cycles each involving a 10A discharge in a life test. The results are shown in Table 18.

                  TABLE 18    ______________________________________                                       Capacity                                       Retention                                       Rate    Battery  10 A Discharge                           150 A Discharge                                       after 500    No.     V         Ah     V        Ah   Cycles (%)    ______________________________________    21B     1.26      122    1.19     119  94    22B     1.24      120    1.18     118  93    23B     1.23      119    1.17     114  92    24B     1.21      115    1.14     109  90    25B     1.12      107    1.01     96   87    26B     1.10      105    1.01     94   86    27B     1.10      103    0.97     92   85    ______________________________________

It has become apparent from the foregoing results that the batteryelectrode substrate of the present invention exhibits excellentproperties.

EXAMPLE 10

Sample 22 of Example 8 was used to form substrates with varied Ni filmthicknesses, which were used to produce Ni-hydrogen batteries accordingto the same procedure as in Example 9. They were examined with respectto capacity retention rate after 500 cycles each involving a 10 Adischarge. The results are shown in Table 19.

                  TABLE 19    ______________________________________    Ni Film       Capacity Retention    Thickness (μm)                  Rate (%)    ______________________________________    0.02          81    0.2           90    1.5           94    4.5           94    ______________________________________

EXAMPLE 11

48.5 wt. % of an Fe₂ O₃ powder as shown in Table 20 was blended with 1.5wt. % of a graphite powder of 2 μm in an average particle size, 10 wt. %of an acrylic resin, 2 wt. % of carboxymethylcellulose and 38 wt. % ofwater. The blend was mixed with a ball mill for 12 hours to prepare aslurry. Subsequently, a polyurethane foam of 2.5 mm in thickness whereinthe number of pores per inch was about 50 was dipped in the slurry,stripped of an excess of the attached component by roll squeezing, anddried in the air at 120° C. for 5 minutes to prepare a porous resincoated with the Fe₂ O₃ powder, which was then heat-treated in a hydrogenstream at 1,070° C. for 5 minutes for sintering to form a porous Febody. The properties of such porous Fe bodies were evaluated. Theresults are shown in Table 21.

                  TABLE 20    ______________________________________    Sample No.  Average Particle Size (μm)    ______________________________________    28          0.7    29          2.2    30          16    31          110    ______________________________________

                  TABLE 21    ______________________________________          Carbon           Electric Tensile    Sample          Content  Porosity                           Resistance                                    Strength                                            Elongation    No.   (wt. %)  (%)     (mΩ/100 mm)                                    (kg/15 mm)                                            (%)    ______________________________________    28    0.03     95      51       3.5     4.8    29    0.04     94      54       3.3     4.4    30    0.06     93      62       2.3     2.5    31    0.03     90      91       1.2     1.0    ______________________________________     Electric Resistance: electric resistance for a width of 10 mm and a lengt     of 100 mm.

Samples shown in Table 21 were Ni-plated in an Ni electroplating Wattsbath at an electric current density of 12 A/dm² to form Ni films of 3 μmin thickness. The properties of the resulting samples are shown in Table22.

                  TABLE 22    ______________________________________          Carbon           Electric Tensile    Sample          Content  Porosity                           Resistance                                    Strength                                            Elongation    No.   (wt. %)  (%)     (mΩ/100 mm)                                    (kg/15 mm)                                            (%)    ______________________________________    28    0.03     94      38       3.7     4.9    29    0.04     93      41       3.5     4.4    30    0.06     92      55       2.6     2.3    31    0.03     89      73       1.3     1.2    ______________________________________     Electric Resistance: electric resistance for a width of 10 mm and a lengt     of 100 mm.

Subsequently, Ni-hydrogen batteries were produced according to the sameprocedure as in Example 9, and the properties thereof were evaluated.The results are shown in Table 23.

                  TABLE 23    ______________________________________                                      Capacity                                      Retention                           150        Rate               10 A Discharge                           A Discharge                                      after 500    Battery No.              V        Ah     V      Ah   Cycles (%)    ______________________________________    28B       1.25     123    1.20   120  94    29B       1.24     121    1.18   119  93    30B       1.21     116    1.14   110  92    31B       1.14     110    1.09   104  91    ______________________________________

EXAMPLE 12

Next, porous Fe bodies were formed according to substantially the sameprocedure as in Example 11 except that the amounts of the Fe₂ O₃ powderand the carbon powder to be blended were varied as shown in Table 24.The Fe₂ O₃ powder used herein was one of 0.7 μm in an average particlesize. The properties of the porous Fe bodies obtained are shown in Table25.

                  TABLE 24    ______________________________________                  Amt. of Fe.sub.2 O.sub.3                             Amt. of Carbon    Sample No.    (wt. %)    (wt. %)    ______________________________________    32            49.97      0.03    33            47         3    34            37         13    ______________________________________

                  TABLE 25    ______________________________________          Carbon           Electric Tensile    Sample          Content  Porosity                           Resistance                                    Strength                                            Elongation    No.   (wt. %)  (%)     (mΩ/100 mm)                                    (kg/15 mm)                                            (%)    ______________________________________    32    0.03     95      63       2.7     2.8    33    0.08     95      50       3.3     4.4    34    0.17     95      85       3.3     1.7    ______________________________________     Electric Resistance: electric resistance for a width of 10 mm and a lengt     of 100 mm.

Subsequently, the samples shown in Table 25 were Ni-plated in an Nielectroplating Watts bath at an electric current density of 10 A/dm² toform Ni films of 2.5 μm in thickness. The properties of the resultingsamples are shown in Table 26.

                  TABLE 26    ______________________________________          Carbon           Electric Tensile    Sample          Content  Porosity                           Resistance                                    Strength                                            Elongation    No.   (wt. %)  (%)     (mΩ/100 mm)                                    (kg/15 mm)                                            (%)    ______________________________________    32    0.03     94      56       2.9     2.9    33    0.08     94      39       3.7     4.6    34    0.17     94      71       3.3     2.1    ______________________________________     Electric Resistance: electric resistance for a width of 10 mm and a lengt     of 100 mm.

Subsequently, Ni-hydrogen batteries were produced according to the sameprocedure as in Example 9, and the properties thereof were evaluated.The results are shown in Table 27.

                  TABLE 27    ______________________________________                                    Capacity                                    Retention                         150        Rate    Battery  10 A Discharge                         A Discharge                                    after 500    No.     V        Ah     V      Ah   Cycles (%)    ______________________________________    32B     1.22     121    1.17   118  94    33B     1.25     125    1.20   120  94    34B     1.19     119    1.14   112  93    ______________________________________

EXAMPLE 13

An Fe₂ O₃ powder of 0.6 μm in an average particle size was used toprepare slurries at blending proportions as shown in Table 28. Apolyurethane foam of 3 mm in thickness was dipped in each slurry,stripped of an excess of the attached component by roll squeezing, anddried in the air at 180° C. for 10 minutes to form a porous resin coatedwith the Fe₂ O₃ powder.

Additionally stated, in every sample, the amount of slurry applied wascontrolled in such a way that the areal density of the resulting porousFe body was 500 g/m².

                                      TABLE 28    __________________________________________________________________________             Binder Resin        Amount                                     Amount        Amount      Residual                          Blended                                 of CMC                                     of Water    Sample        of Fe.sub.2 O.sub.3                    Carbon Rate                          Amount Blended                                     Blended    No. (wt. %)             Material                    a (%) (wt. %)                              a × b                                 (wt. %)                                     (wt. %)    __________________________________________________________________________    35  60   phenolic resin                    60    12  12 2   26    36  60   phenolic resin                    60     8  8  2   30    37  60   phenolic resin                    40    10  6.7                                 2   28    38  60   phenolic resin                    40     8  5.3                                 2   30    39  60   phenolic resin                    40     4  2.7                                 2   34    40  60   epoxy resin                    10    20  3.3                                 2   18    __________________________________________________________________________

Subsequently, they were heated to 1,150° C. at a heat-up rate of 200°C./min in an N₂ stream, heat-treated at 1,150° C. for 5 minutes, andthen heat-treated in a H₂ +N₂ mixed gas (mixing ratio: 1:3) stream at1,150° C. for 5 minutes to obtain porous Fe bodies.

Additionally stated, the heat treatment was continuously effected usinga mesh belt type continuous heat treatment furnace, the heating zone ofwhich had an N₂ gas atmosphere in the first half portion thereof and aH₂ +N₂ gas atmosphere in the second half portion thereof. The propertiesof the porous Fe bodies obtained were evaluated. The results are shownin Table 29.

                  TABLE 29    ______________________________________          Carbon          Electric Tensile    Sample          Content Porosity                          Resistance                                   Strength                                           Elongation    No.   (wt. %) (%)     (mΩ/100 mm)                                   (kg/15 mm)                                           (%)    ______________________________________    35    0.25    95      75       0.9     1.3    36    0.02    95      48       2.3     4.3    37    0.02    95      47       2.1     4.5    38    0.01    95      54       1.8     4.2    39    0.01    95      69       1.3     1.8    40    0.01    95      71       1.1     1.1    ______________________________________     Electric Resistance: electric resistance for a width of 10 mm and a lengt     of 100 mm.

Subsequently, the samples shown in Table 29 were Ni-plated in an Nielectroplating Watts bath at an electric current density of 5 A/dm² toform Ni films of 1.1 μm in thickness. The properties of the resultingsamples are shown in Table 30.

                  TABLE 30    ______________________________________          Carbon          Electric Tensile    Sample          Content Porosity                          Resistance                                   Strength                                           Elongation    No.   (wt. %) (%)     (mΩ/100 mm)                                   (kg/15 mm)                                           (%)    ______________________________________    35    0.25    94      70       1.2     1.2    36    0.02    94      39       2.9     4.4    37    0.02    94      38       2.5     4.6    38    0.01    94      40       2.3     4.3    39    0.01    94      62       1.5     1.7    40    0.01    94      64       1.2     1.2    ______________________________________     Electric Resistance: electric resistance for a width of 10 mm and a lengt     of 100 mm.

Subsequently, Ni-hydrogen batteries were produced according to the sameprocedure as in Example 9, and the properties thereof were evaluated.The results are shown in Table 31.

                  TABLE 31    ______________________________________                                   Capacity Retention    Battery           10 A Discharge                       150 A Discharge                                   Rate after    No.    V       Ah      V     Ah    500 Cycles (%)    ______________________________________    35B    1.18    117     1.13  111   90    36B    1.24    125     1.21  119   94    37B    1.24    124     1.20  120   94    38B    1.24    125     1.20  121   94    39B    1.19    118     1.12  112   92    40B    1.17    116     1.11  110   89    ______________________________________

It has become apparent from the foregoing results that the batteryelectrode substrate of the present invention is excellent.

As described hereinbefore, according to the present invention, a batteryelectrode substrate decreased in residual carbon content and havingexcellent mechanical strength properties and electrical properties canbe obtained at a low production cost.

What is claimed is:
 1. A battery electrode substrate for use in abattery collector, the battery electrode substrate being constituted ofa porous metallic body structure having communicating pores at aporosity of at least 90% and an Fe/Ni multilayer structure wherein theskeletal portion of the porous metallic body has been produced usingiron oxide as the starting material and is composed of Fe, has a carboncontent of at most 0.2% and has an Ni covering layer on the surfacethereof while pores communicating with the inside and outside of Feskeletal portion exist in the Fe skeletal portion and the inside of thepores is covered with Ni.